Title: Multi-Agent Multi-Game Entity Transformer. Abstract: Building large-scale generalist pre-trained models for many tasks is becoming an emerging and potential direction in reinforcement learning (RL). Research such as Gato and Multi-Game Decision Transformer have displayed outstanding performance and generalization capabilities on many games and domains. However, there exists a research blank about developing highly capable and generalist models in multi-agent RL (MARL), which can substantially accelerate progress towards general AI. To fill this gap, we propose Multi-Agent multi-Game ENtity TrAnsformer (MAGENTA) from the entity perspective as an orthogonal research to previous time-sequential modeling. Specifically, to deal with different state/observation spaces in different games, we analogize games as languages, thus training different "tokenizers" for various games. The feature inputs are split according to different entities and tokenized in the same continuous space. Then, two types of transformer-based model are proposed as permutation-invariant architectures to deal with various numbers of entities and capture the attention over different entities. MAGENTA is trained on Honor of Kings, Starcraft II micromanagement, and Neural MMO with a single set of transformer weights. Extensive experiments show that MAGENTA can play games across various categories with arbitrary numbers of agents and increase the efficiency of fine-tuning in new games and scenarios by 50\%-100\%. See our project page at \url{https://sites.google.com/view/rl-magenta}.